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The composition of gas produced by the gasification of refuse-derived fuel (RDF) can be affected by the content of individual components of RDF and their mutual interactions. In this work, plastics, paper, wood, textile and RDF were gasified in a two-stage gasification system and the obtained tar yields and product gas quality were compared. The two-stage reactor consisted of an air-blown gasifier and a catalytic reactor filled with carbonized tire pyrolysis char as the tar-cracking catalyst. Tire pyrolysis char is a promising alternative to expensive catalysts. The impact of temperature and catalyst amount on the tar yield and gas composition was investigated. Theoretical oxygen demand for all material classes was calculated and its effect on gas composition and tar yield is discussed. The results indicate that the gasification of plastics produces the highest amount of tar and hydrocarbon gases, while the CO2 content of the product gas remains the lowest compared to all other materials. On the other hand, the paper fraction produced hydrogen-rich gas with low tar content. The gasification of RDF at 700 °C provided the lowest tar yield compared to all other materials, indicating positive synergic effects of lignocellulosic biomass and plastics in tar reduction. The significance of these interactions was suppressed at the highest temperature of 900 °C, as the thermal cracking of tar became dominant. For CO2 content, a negative synergic effect (higher CO2 concentration) was observed.

Municipal solid waste constitutes one of the major challenges and concerns of our society. Disposal of waste material is potentially dangerous, harming both environment and mankind. In order to diminish negative effects of municipal solid waste, its thermal decomposition to valuable chemicals has been studied. The principal draw-back of thermal processes used for solid waste utilization as raw material is tar formation. In this study, low-cost catalysts of different origin were tested in the decomposition of a model component of tar originating from waste material pyrolysis/gasification. p-Xylene was selected as the model compound found in biomass decomposition products. Its decomposition was carried out in the presence of either tire pyrolysis char- or clay minerals-based catalysts. Tar-cracking activities of both catalyst types at varying experimental conditions were compared and related to the catalysts physical-chemical properties. In experiments, either empty reactor or reactor filled with 10 g of the catalyst was used; p-xylene mass flow was set to 2.58 g h−1 (50 μL min−1, room temperature), and decomposition temperature ranging from 750 °C to 850 °C was applied. Moreover, evolution of the output variables, p-xylene conversion and hydrogen content in the gas phase, with the reaction time was investigated. Catalysts’ properties were assessed based on nitrogen adsorption isotherms, thermogravimetric and elemental composition analyses. Amounts and composition of p-xylene catalytic decomposition products were evaluated using GC analysis of both gaseous phase and condensable products. Results showed the superiority of tire pyrolysis char catalyst over that based on clay minerals.

Gasification is a promising technology for the conversion of mixed solid waste like refuse-derived fuel (RDF) and municipal solid waste (MSW) into a valuable gas consisting of H2, CO, CH4 and CO2. This work aims to identify the basic challenges of a single-stage batch gasification system related to tar and wax content in the producer gas. RDF was first gasified in a simple semi-batch laboratory-scale gasification reactor. A significant yield of tars and waxes was received in the produced gas. Waxes were analyzed using gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectrometry. These analyses indicated the presence of polyethylene and polypropylene chains. The maximum content of H2 and CO was measured 500 seconds after the start of the process. In a second series of experiments, a secondary catalytic stage with an Ni-doped clay catalyst was installed. In the two-stage catalytic process, no waxes were captured in isopropanol and the total tar content decreased by approximately 90 %. A single one-stage semi-batch gasification system is not suitable for RDF gasification; a large fraction of tar and waxes can be generated which can cause fouling in downstream processes. A secondary catalytic stage can significantly reduce the tar content in gas.